Doctor Decoded: Infectious vs. Contagious

Not *all* infections are contagious.

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Your doctor assures you your infection isn’t contagious, and your friends and loved ones are safe. But … aren’t infectious and contagious the same thing? 

These two terms certainly have a big overlap, but they’re not interchangeable. Infectious refers to any type of disease caused by pathogens, such as bacteria and viruses

When these pathogens enter the body, they hijack your body’s cells and multiply rapidly. Meanwhile, you’ll be stuck dealing with unpleasant symptoms—like a runny nose (for the common cold), pressure in your face (for a sinus infection), or painful urination (for a urinary tract infection)—until your immune system can fight off the pathogen.  

Contagious is a disease that can spread from person to person, usually from direct contact with an infected person, or something they have touched. Some diseases are so contagious, however, that you can get sick just from being in the same room as an infected person, even minutes after they have left.

Most infectious diseases are contagious—like the flu, measles, and strep throat—but not all. Think of Lyme disease, for example. This is an infectious disease that is caused by the bacterium Borrelia burgdorferi. However, it’s not contagious because it’s spread by ticks, not humans. Once you’re infected, you can’t transmit it to your mom, coworker, or the man next to you on the bus. 

Another thing both infectious and contagious diseases have in common? They’re typically preventable, and good handwashing habits can reduce your risk for many infections.